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IS 14674 (1999) : High Voltage Alternating Current
Circuit-breakers-guide for Seismic Qualification of High
Voltage Alternating Current Circuit-breakers [ETD 8: High
Voltage Switchgear and Controlgear]
Satyanarayan Gangaram Pitroda
Invent a New India Using Knowledge
5fR TT^ ^TT <sMHI | *ft ^fft ^TRT ^ff ^TT ^T^fT )f
Bhartrhari — Nltisatakam
"Knowledge is such a treasure which cannot be stolen"
PROTECTED BY COPYRIGHT
IS 14674: 1999
IEC 1166 (1993)
„ ( Reaffirmed 2004 )
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HIGH VOLTAGE ALTERNATING CURRENT
CIRCUIT-BREAKERS— GUIDE FOR SEISMIC
QUALIFICATION OF HIGH VOLTAGE
ALTERNATING CURRENT CIRCUIT-BREAKERS
BUREAU OF INDIAN STANDARDS
MAN A KB HA VAN, 9 BAHADUR SHAH ZAFAR MARG
NEW DELHI 110002
June 1999 Price Group 7
High Voltage Switchgear and Controlgear Sectional Committee, ET 08
This Indian Standard which is identical with IEC 1166 (1993) 'High-voltage alternating current circuit-
breakers — Guide for seismic qualification of high-voltage alternating current circuit-breakers', issued by
the International Electrotechnical Commission (IEC), was adopted by the Bureau of Indian Standards on
the recommendations of the High Voltage Switchgear and Controlgear Sectional Committee (ET 08) and
approval of the Electrotechnical Division Council. It is a guide that specifies seismic severity levels and
provides procedures to seismically qualify only those HV alternating current circuit breakers which are
The text of the IEC 1166 (1993) has been approved as suitable for publication as Indian Standard
In the adopted standard, certain terminology and conventions are not identical to those used in Indian
Standards. Attention is specially drawn to the following:
a) Wherever the words 'International Standard' appear referring to this standard, they should be read
as Sndian Standard'.
b) Comma (,) has been used as a decimal marker while in Indian Standards, the current practice is
to use a point (.) as the decimal marker.
In this adopted standard, reference appears to certain International Standards for which Indian Standards
also exit. The corresponding Indian Standards which are to be substituted in their place are listed below
along with their degree of equivalence for the editions indicated:
IEC 50 (441): 1984
Vocabulary — Chapter 441 :
Switchgear, controlgear and
IS 1885 (Part 17): 1979
IEC 56 : 1 987 High - voltage
IS 13118: 1991
Environmental testing —
Part 1 : General and guidance
IS 9000 (Parti): 1988
& IS 9001 (Parti): 1984
IEC 68-2-6:1982 Environmental
testing — Part 2 : Tests — Test Fc
and guidance: Vibration
IS 9000 (Part 8): 1981
& IS 9000 (Part 13) :1979
(Continued on third cover)
IS 14674 : 1999
HIGH VOLTAGE ALTERNATING CURRENT CIRCUIT-BREAKERS -
GUIDE FOR SEISMIC QUALIFICATION OF HIGH-VOLTAGE
ALTERNATING CURRENT CIRCUIT-BREAKERS
1 Scope and object
This International Standard applies only to ground mounted high-voltage (HV) circuit-
breakers, the supporting structures of which are rigidly connected with the ground, and
does not cover the seismic qualification of circuit-breakers in metal enclosed switchgear.
The seismic qualification of the HV circuit-breakers shall take into account any auxiliary and
control equipment which is mounted on the circuit-breaker structure. If the auxiliary and
control equipment is mounted on a separate structure, it may be qualified independently.
This standard is a guide providing procedures to seismically qualify HV alternating-current
ground mounted circuit-breakers. It is mainly based on IEC 68-3-3, which in turn refers to
IEC 68-1. IEC 68-2-6, IEC 68-2-47 and IEC 68-2-57.
The seismic qualification of a circuit-breaker is only performed upon request.
This standard specifies seismic severity levels and gives a choice of methods that can be
applied to demonstrate the performance of HV circuit-breakers for which seismic qualifi-
cation is required.
2 Normative references
The following normative documents contain provisions which, through reference in
this text, constitute provisions of this International Standard. At the time of publication,
the editions indicated were valid. All normative documents are subject to revision, and
parties to agreements based on this International Standard are encouraged to investigate
the possibility of applying the most recent editions of the normative documents indicated
below. Members of IEC and ISO maintain registers of currently valid International
IEC 50(441): 1984, International Electrotechnical Vocabulary (IEV), Chapter 441: Switch-
gear, controlgear and fuses
IEC 56: 1987, High-voltage alternating-current circuit-breakers
IEC 68-1 : 1988, Environmental testing - Part 1: General and guidance
IEC 68-2-6: 1982, Environmental testing - Part 2: Tests - Test Fc and guidance:
IEC 68-2-47: 1982, Environmental testing - Part 2: Tests - Mounting of components,
equipment and other articles for dynamic tests including shock (Ea), bump (Eb), vibration
(Fc and Fd) and steady-state acceleration (Ga) and guidance
IEC 68-2-57: 1989, Environmental testing - Part 2: Tests - Test Ff. Vibration - Time
IEC 68-3-3: 1991, Environmental testing - Part 3: Background information. Seismic test
methods for equipment.
IS 14674 : 1999
For definition of the terms used in this International Standard refer to IEC 68-3-3.
4 Seismic qualification requirements
The seismic qualification should demonstrate the circuit-breaker's ability to withstand
seismic stress and to maintain its specified function, both during and after the seismic
The most commonly used methods are:
a) qualification by test;
b) qualification by combined test and analysis.
NOTE - Qualification by pure analysis is acceptable if sufficient information on physical parameters (e.g.
damping coefficient) and on the functional behaviour of the circuit-breaker is available.
The severity levels shall be chosen from table 1 .
Table 1 - Seismic qualification levels - horizontal severities
For vertical severities the direction factor (D) is 0,5 (see IEC 68-3-3).
1 The required response spectrum of qualification level AF5 covers, in the range of predominant seismic
frequency of 1 Hz to 35 Hz, the following response spectra: Endesa, Edelca, USA/NRC RG 1.60. Newmark
Design Response Spectra (scaled to 5 m/s*), Nema (5 m/s 2 max. foundation acceleration), Oept. of Water &
Power Los Angeles, San Diego SDG & E Imperial Substation.
2 Information on the correlation between seismic qualification levels and different seismic scales is given
in 8.2.4 of IEC 68-3-3.
The selected qualification level should be in accordance with expected earthquakes at
maximum ground motions for the location of installation. This level corresponds to S2
earthquake (see 3.24 of IEC 68-3-3).
IS 14674 : 1999
6 Qualification by test
6. 1 Introduction
The test procedure for qualification of a circuit-breaker by test should be in accordance
with clauses 1 1 to 15 of IEC 68-3-3.
The tests shall be made at the ambient air temperature of the test location; this tem-
perature shall be recorded in the test report.
The qualification shall be carried out:
- on a complete circuit-breaker when all poles are mounted on the same supporting
- on one pole in the case of a circuit-breaker with three separate poles;
- on one column with its interrupters in the case of multibreak poles on separate
NOTE - If a circuit-breaker cannot be tested with its supporting structure (e.g., due to its size), the
dynamic contribution of the structure should be determined by analysts.
The circuit-breaker shall be tested in the closed position except when the open position
has been shown to be more critical during the vibration response investigation.
General mounting requirements are given in IEC 68-2-47. The circuit-breaker shall be
mounted as in service including dampers (if any).
NOTE - For more detailed guidance in case of equipment normally used with vibration isolators (see A. 5,
The horizontal orientation of the circuit-breaker should be in the direction of excitation
acting along its two main orthogonal axes.
Any fixtures or connections required only for testing should not affect the dynamic
behaviour of the circuit-breaker.
The method of mounting of the circuit-breaker shall be documented and shall include a
description of any interposing fixtures and connections.
6.3 External load
Generally, electrical and environmental service loads cannot be simulated during the
seismic test. This applies also to internal pressure of the circuit-breaker due to safety
requirements of the test laboratory.
NOTE - For combination of seismic and service loads, see clause 8.
The circuit-breaker shall not be operated during the seismic tests; the control and auxiliary
circuits shall be energized to monitor any chattering of relays, but they need not cause the
circuit-breaker to operate.
IS 14674 :1999
Measurements should be performed in accordance with 5.2 of IEC 68-3-3, and should
- vibration motion of the center of gravity (when applicable);
- strains on critical elements (e.g. porcelains).
6.5 Frequency range
The frequency range shall be 0,5 Hz to 35 Hz.
6.6 Test severity
The test severity shall be chosen in accordance with clause 5.
The recommended required response spectra are given in figures 1 to 3 for the different
seismic qualification levels. The curves relate to 2 %, 5 %, 10 % and 20 % or more damp-
ing ratio of the circuit-breaker.
Spectra for different damping values can be obtained by linear interpolation.
The time-history test method is to be preferred, since it more closely simulates actual
conditions, particularly if the behaviour of the circuit-breaker under test is not linear. The
test method should be in accordance with IEC 68-2-57.
6.6.1 Parameters for sine-beat excitation
Test frequencies shall cover the frequency range stated in 6.5 with 1/2 octave spacing.
For each test frequency five sine-beats of five cycles each are applied.
6.6.2 Parameters for time-history excitation
The total duration of the time-history shall be about 30 s of which the strong part shall be
not less than 6 s.
6.7.1 Test directions
The test directions should be chosen according to 3.19 of IEC 68-3-3.
In some cases the effect of the vertical acceleration results in negligible stresses and the
vertical excitation may be omitted.
6.7.2 Test sequence
The test sequence shall be as follows:
- functional checks before testing;
- vibration response investigation (required to determine damping and/or for
- seismic qualification test, and
- functional checks after testing.
IS 14674 : 1999
188.8.131.52 Functional checks
Before and after the tests the following operating characteristics or settings shall be
recorded or evaluated (when applicable) at the rated supply voltage and operating
a) closing time;
b) opening time;
c) time spread between units of one pole;
d) time spread between poles (if multipole tested);
e) gas and/or liquid tightness;
f) other important characteristics or settings as specified by the manufacturer.
184.108.40.206 Vibration response investigation
The vibration response investigation shall be carried out according to 10.1 and 14.2 of
IEC 68-3-3 over the frequency range stated in 6.5.
220.127.116.11 Seismic qualification test
The test shall be performed by applying one of the procedures stated in flow chart A3
(except test Fc) or flow chart A4 of annex A of IEC 68-3-3 depending on the test facilities.
The test shall be performed once at the level chosen in clause 5.
During the seismic test the following parameters shall be recorded:
- strain of critical components such as post insulators and support structure;
- deflection at terminal;
- electrical continuity of the main circuit;
- electrical continuity of the auxiliary and control circuit.
7 Qualification by combined test and analysis
7. 1 Introduction
The method may be used:
- to qualify a circuit-breaker which cannot be qualified by testing alone (e.g. because
of its size and/or complexity);
- to qualify a circuit-breaker already tested under different seismic conditions;
- to qualify a circuit-breaker similar to a circuit-breaker already tested but which
includes modifications influencing the dynamic behaviour (e.g. change in the length of
insulators or in the mass of interrupters);
- to qualify a circuit-breaker if its vibrational and functional data are known.
IS 14674 : 1999
7.2 Vibrational and functional data
Vibrational data (damping, critical frequencies, stresses of critical elements as a function
of input acceleration) for analysis can be obtained by:
a) a dynamic test of a similar circuit-breaker;
b) a dynamic test at reduced test level;
c) determination of critical frequencies and damping by other tests such as free
oscillation tests or low level excitation (see annex A).
Functional data should be obtained from test performed on a similar circuit-breaker.
The general procedure is:
a) to establish, using experimental data stated in 7.2, a mathematical model of the
circuit-breaker in order to assess its dynamic characteristics;
b) to determine the response, in the frequency range stated in 6.5, using either of the
methods described in the following subclauses, but other methods may be used if they
7.3. 1 Acceleration time-history method of calculation
When the time-history method is employed for seismic analysis, the ground motion
acceleration time-histories shall comply with the RRS (see table 1). Two types of super-
imposition may generally be applied depending on the complexity of the problem:
a) separate calculation of the maximum responses due to each of the three
components (x and y in the horizontal, and z in the vertical direction) of the earthquake
motion. The effects of each single horizontal direction and the vertical direction shall
be combined by taking the square root of the sum of the squares, i.e. (x 2 + z 2 )** and
(y 2 + z*) V2 . The greater of these two values is used for dimensioning the circuit-breaker.
b) simultaneous calculation of one of the horizontal directions and the vertical direction
(x with z) and thereafter calculation of the other horizontal direction and the vertical
direction (y with z). This means that after each time step of calculation all values
(forces, stresses) are superimposed algebraically. The greater of these two values is
used for dimensioning the circuit-breaker.
7.3.2 Modal analysis using the required response spectrum (RRS)
When the response spectra method is used for seismic analysis, the procedure of
combining the stresses is hereinafter described for an orthogonal system of coordinates
in the main axes of the circuit-breaker and with x and y in the horizontal and z jn the
vertical direction. The maximum values of stresses in the circuit-breaker for each of
the three directions x. y and z are obtained by super-imposing the stresses calculated for
the various modal frequencies in each of these directions by taking the square root of
the sum of the squares. The maximum values in the x and z direction - and in the y and z
direction - are combined by taking the square root of the sum of the squares. The greater
value of these two cases (x, z) or (y, z) is the dimensioning factor for the circuit-breaker.
IS 14674 :1999
7.3.3 Static coefficient analysis
This method is adopted for rigid equipment. It may also be used for flexible equipment,
as an alternate method of analysis; this allows a simpler technique in return for added
conservatism. No determination of natural frequencies is made but, rather, the response
spectrum of the circuit-breaker is assumed to be the peak of the required response
spectrum at a conservative and justifiable value of damping. This response is then multi-
plied by a static coefficient of 1 ,5 which has been established from experience to take into
account the effects of both multifrequency excitation and multimode response. A lower
static coefficient may be used if it can be shown to yield conservative results.
The seismic forces on each part of the HV circuit-breaker are obtained by multiplying the
values of the mass, concentrated at its center of gravity, and the acceleration.
The resulting force should be distributed proportionally to the mass distribution.
The stress analysis may then be completed as stated in 8.1.
8 Evaluation of the seismic qualification
8.1 Combination of stresses
The seismic stresses determined by test or analysis shall be combined with other service
loads to determine the total withstand capability of the circuit-breaker.
The probability of an earthquake of the recommended seismic qualification level occurring
during the life-time of the circuit-breaker is low, whilst the maximum seismic load in a
natural earthquake would only occur if the circuit-breaker is excited at its critical
frequencies with maximum acceleration. As this will last only a few seconds, a combi-
nation of the utmost electrical and environmental service loads wouid lead to unrealistic
The following loads are considered to occur simultaneously, if not otherwise specified:
- internal pressure;
- static terminal load.
NOTE - See the values given in 18.104.22.168 of IEC 56. Multiply the static terminal load by 0,7, to take into
account a wind velocity of only 10 m/s on connected conductors.
- wind force of 10 m/s on the circuit-breaker;
- seismic forces.
The stresses due to the combination of these loads shall be equal to or less than
the guaranteed minimum bending stress of each of the considered critical elements (e.g.
The combination of loads can be done by static analysis (see figure 4).
IS 14674 : 1999
8.2 Acceptance criteria of the seismic simulation
The seismic simulation waveforms shall produce a test response spectrum which
envelopes the required response spectrum (calculated at the same damping ratio) and
have a peak acceleration equal to or greater than the zero period acceleration.
8.3 Functional evaluation of the test results
Functional results are normally obtained only by dynamic tests. These results may be
extrapolated to obtain qualification by combination of tests and analysis. In particular:
a) the main contacts shall remain in position during the seismic test;
b) chatter of relays shall not cause the circuit-breaker to operate;
C) chatter of relays shall not provide wrong information of the status of the circuit-
breaker (position, alarm signals).
NOTE - Normally, chatter of relays during less than 5 ms is considered to be acceptable.
d) resetting of monitoring equipment is considered to be acceptable if the overall
performance of the circuit-breaker is not affected;
e) no significant change should occur in functional checks recordings at the end of the
test sequence compared with the initial ones (see 22.214.171.124).
9.1 Information for seismic qualification
The following information is required for either analysis or testing of the circuit-breaker:
1) Severity (clause 5).
2) Details of mounting (6.2).
3) Number and relative position of testing axes.
9.2 Test report
The test report shall contain:
1) Circuit-breaker identification file including mounting details.
2) Information for seismic qualification.
3) Test facility:
b) test equipment description and calibration.
4) Test method and procedures.
5) Test data including functional data (see 126.96.36.199 and 7.2).
6) Results and conclusions
7) Approved signature and date.
9.3 Analysis report
Analysis, which is included as a proof of performance, should have a step-by-step pre-
IS 14674 : 199S
0,1 0.2 0.5 1 2 5 10 20
NOTE • According to IEC 68-3-3, the value of g is rounded up to the nearest unity, that is 10 m/s 2 .
Figure 1 - RRS for ground mounted equipment.
Qualification level: AF5: ZPA - 5 m/s 2 (0.5 fl)
IS 14674 : 1999
NOTE - According to IEC 68-3-3, the value of g is rounded up to the nearest unity, that is 10 m/s*.
Figure 2 - rrs for ground mounted equipment.
■Qualification level: AF3: ZPA '- 3 m/s 2 (0,3 g)
IS 14674 : 1999
2 5 10 20
et plus / and more
NOTE • According to IEC 68-3-3, the value of g is rounded up to the nearest unity, that is 10 m/s 2 -.
Figure 3 - RRS for ground mounted equipment.
Qualification level AF2: ZPA « 2 m/s 2 (0,2 g)
IS 14674 : 1999
Supporting insulatorstress at A-A
p W 8
Stresses due at:
- p internal pressure
- w wind pressure on the circuit breaker
- F static terminal load
- s seismic force
- F maximum permissible bending stress
Figure 4 - Example for combination of stresses
IS 14674 :1999
I ;..■■■ .- / .- .- .- ,- ■ i .- : i j ~- VyrzTTr^zz
1 X^^^^M^^^^^^M^^j^^^i W\
n + li
__n = 7_|
::*_"Ur: Typical case of free oscillations
...:,.i Note: "n" designs the number of cyc les gf
— I— j— — '— -
— Y^/Y, values TJf;
Figure 5 - Graph for determining the clamping ratio
IS 14674 :1999
Characterization of the equipment
A.1 Low level excitation
The method combines testing and analysis and utilizes the application of excitation at
points in the circuit-breaker with low level excitation for response determination.
A. 1.1 Test method
With the circuit-breaker mounted to simulate the recommended service mounting condi-
tions, a number of portable exciters are attached at the points on the circuit-breaker which
will best excite its various modes of vibration.
The data obtained from the monitoring instruments placed on the circuit-breaker can be
used to analyze the circuit-breaker's seismic performance.
A. 1.2 Analysis
The frequency response functions obtained from the test can be used to determine
the modal frequencies and damping which may be used in a dynamic analysis of the
circuit-breaker. This method provides a greater degree of certainty in analysis since
the analytical model can be refined to reflect the measured natural frequencies and experi-
mental damping ratios can be used.
A. 1.3 Qualification
This method can adequately qualify the circuit-breaker in either of two ways, namely:
- the circuit-breaker can be excited to a level at least equal to the expected response
from a design earthquake, using analysis to justify the excitation;
- the test data on modal frequencies can be used in a mathematical model to verify
The first method is based upon the equivalence between the effects due to the base
excitation (earthquake) and the concentrated force excitation. The equivalence is obtained
if the circuit-breaker responses give the same relative displacements in the two cases.
A.2 Free oscillation test
A.2.1 Natural frequency determination
To determine the natural frequency (first vibration mode) of the circuit-breaker, the circuit-
breaker, fully furnished for service, shall be fixed to a rigid foundation by the means
provided for in its design. A tensile force, of value not less than one-third of the weight of
the oscillating equipment, shall be applied along the direction of maximum probable ampli-
tude, in the vicinity of the center of gravity of the circuit-breaker. The oscillations of the
circuit-breaker shall be recorded when this force is suddenly released.
IS 14674 : 1999
A.2.2 Damping ratio determination
To determine the clamping ratio of the circuit-breaker, the same test may be used but, in
this case, the recording of the oscillations shall be made with suitable sensitivity and
accuracy to determine the decrement of the oscillations as a function of time. The equi-
valent damping ratio is determined using the monogram in figure 5, from the sequence of
peaks in the recorded wave, in that range of the record in which the logarithmic decrement
appears most clear.
A.2.3 Special cases in the natural frequency and damping ratio determination
When the circuit-breaker consists of different elements, each one susceptible to vibration,
the tests in A.2.1 and A.2.2 shall be made by applying tensile force around the centre of
gravity of each of the several masses subject to vibration and simultaneously recording
the oscillation of those points corresponding to the greatest amplitude, while attempting
to detect all the modes of oscillation in the arrangement. In such cases, it is possible that
the record of oscillations in one element is influenced by the oscillations of some
other element with a nearby frequency, in which case the determination shall be made as
described in the sketch of the top of figure 5.
(Continued from second cover)
IS 9001 (Part 12): 1979
I EC 68-2-47: 1982
Environmental testing — Part 2 :
Tests — Mounting of components,
equipment and other articles for
dynamic tests including shock (Ea),
bump (Eb), vibration (Fc and Fd)
and steady state acceleration
(Ga) and guidance
I EC 68-2-57 : 1989 Environmental No ISS Exists —
testing — Part 2 : Tests — Test Ff.
Vibration — Time history method
IEC 68-3-3: 1991 Environmental No ISS Exists —
testing — Part 3 : Background
information. Seismic test
methods for equipment
Only the English language text in the International Standard has been retained while adopting it in this
For the purpose of deciding whether a particular requirement of this standard is complied with, the final
value, observed or calculated, expressing the result of a test or analysis, shall be rounded off in accordance
with IS 2 : 1960 'Rules for rounding off numerical values (revised)'. The number of significant places
retained in the rounded off value should be the same as that of the specified value in this standard.
Bureau of Indian Standards
BIS is a statutory institution established under the Bureau of Indian Standards Act, 1986 to
promote harmonious development of the activities of standardization, marking and quality cer-
tification of goods and attending to connected matters in the country.
BIS has the copyright of all its publications. No part of these publications may be reproduced in
any form without the prior permission in writing of BIS. This does not preclude the free use, in
the course of implementing the standard, of necessary details, such as symbols and sizes,
type or grade designations. Enquiries relating to copyright be addressed to the Director (Pub-
Review of Indian Standards
Amendments are issued to standards as the need arises on the basis of comments. Standards
are also reviewed periodically; a standard along with amendments is reaffirmed when such
review indicates that no changes are needed; if the review indicates that changes are needed,
it is taken up for revision. Users of Indian Standards should ascertain that they are in posses-
sion of the latest amendments or edition by referring to the latest issue of 'BIS Handbook' and
'Standards: Monthly Additions'.
This Indian Standard has been developed from Doc : No. ET 08 (5012).
Amendments Issued Since Publication
Date of Issue
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